What is the purpose of heat shock in bacterial transformation?

Heat shock is used during bacterial transformation to facilitate the uptake of plasmid DNA by chemically treated bacteria. In this method, bacterial cells are first made competent using a calcium chloride solution, which destabilizes the cell membrane. A sudden increase in temperature (heat shock) creates a thermal imbalance, temporarily opening pores in the cell membrane. This allows foreign DNA to enter the cell. Following the heat shock, the cells are rapidly cooled to reseal the membrane and retain the introduced DNA.